372 NATURAL HISTORY OF AQUATIC INSECTS CH. 



acid or nitrogen, though they quickly become un- 

 conscious and motionless in such gases. 



The saltness of sea-water might be expected to 

 prove disagreeable if not injurious to Insects, but 

 there is little proof that such is actually the case. 

 Insects, when forcibly submerged, survive about as 

 long in salt water as in fresh. Many Insects are not 

 easily wetted by water. The hairs with which some 

 are covered and the dense, glossy chitin of others 

 prevent effectual wetting. The surface-film of water 

 will not pass into small openings, such as the mouth, 

 or the spiracles, or the spaces between close-set Hairs. 

 Larvae however, which live in water, and are tho- 

 roughly wetted by it, cannot endure the change from 

 fresh water to salt. I placed thirteen living Chiro- 

 nomus larvae in salt water, and found that in four 

 hours five had died, while the rest were extremely 

 languid. In eight hours all were dead. By gradual 

 acclimatisation even such larvae as these can make 

 themselves at home in salt water. Packard dredged 

 up live Chironomus larvae in Salem harbour, and not 

 a few Dipterous larvae of various species have been 

 found established in brine-vats. Plateau has drawn 

 up a list 1 of near eighty species of Insects and 

 Arachnida, which, though they cannot swim and 

 though they breathe only gaseous air, inhabit the 

 sea-shore, and undergo daily or at least frequent 

 submersion. The list will no doubt be largely 

 increased by the future labours of naturalists. 



The Insects of the sea-shore are mostly very small. 



1 " Lcs Myriopodes Marins," Jour, de VAnat. et Phys. 



(1890). 



